1. Field of the Invention
The present invention generally relates to plastic laminated bodies, manufacturing methods of the same, and rear projection type image display apparatuses, and more particularly, to a manufacturing method of a plastic laminate body such as a composite plastic molding article made by laminating a plurality of plastics, an optical element having a transfer surface (reflection surface) having high precision like a plastic reflection mirror, or the like.
2. Description of the Related Art
As a method and an apparatus by which two members are laminated and a transfer surface is transferred to one of the members, there are the contact bonding method and the apparatus shown in Japanese Laid-Open Patent Application No. 1-316702. In the method and apparatus, a lens sheet part is heated and made molten so as to be developed and extended on a lens mold surface, and then a translucent member is contact-bonded. In this method, it is necessary to make the lens sheet thick in order to cover the curvature in a case where a subject configuration is a curved surface. Because of this, it is required to take a lot of time for heating, melting, and solidifying the lens sheet, and this causes increasing cost. Furthermore, thicknesses of some parts of the lens sheet become uneven, and therefore it is difficult to apply pressure to the entire transfer surface evenly. Because of this, as shown in FIG. 2, an uneven contraction occurs after the contact bonding process and therefore it is difficult to manufacture a molded article with high precision.
In Japanese Laid-Open Patent Application No. 3-82513, Japanese Laid-Open Patent Application No. 5-154933, Japanese Laid-Open Patent Application No. 7-178834, and Japanese Laid-Open Patent Application No. 2000-326360, a method for providing a reflection film, where a metal layer is formed in advance in a mold, then injecting and filling a resin from a back surface of the reflection film so as to unify, is suggested. In this case, the film has to be fixed in the mold in order to prevent wrinkles from being generated and therefore the mold structure is complex. Furthermore, if it is attempted to make the film correspond to a curved surface, the film is adversely influenced by high temperature at the time of resin injection and flow pressure on the assumption of uniformity by injection molding. This causes generation of wrinkles and tears of the film. If the molded article is made thick for securing strength of the molded article, it takes more time for cooling and the molding cycle increases. Furthermore, if the thickness of the molded article is not uniform, pressure at the thick wall part and pressure at the thin wall part do not become uniform, so that it is difficult to secure high configuration precision only by injection molding.
In Japanese Patent No. 2831959, first, more than two plastic base materials prepared in advance are inserted into the mold, and a transfer due to self expansion and uniformity are realized by heating at a temperature higher than a softening temperature of the plastic base materials. Next, the plastic base materials are cooled so as to have a temperature less than a heat deformation temperature and then pulled out. In this case, although there is no influence of unevenness of resin pressure and resin flow, it takes a lot of time for molding because all of the base material is heated and cooled. This causes an increase of cost.
There is a unifying way by heat contact bonding that can prevent the above-discussed influence by the resin flowing and the increase of the molding cycle, comprising a manufacturing method of a plastic laminate body such as a composite plastic molding article made by laminating a plurality of plastics, including an optical element having a transfer surface (reflection surface) having high precision, such as a plastic reflection mirror.
However, according to the related art unifying way by heat contact bonding, there are the following problems in a case where the subject configuration includes a curved surface.
FIG. 1 is a schematic view showing a related art manufacturing method of a plastic laminate body. More specifically, related art wherein two members are bonded in one body by heat contact bonding and a transfer surface is transferred to either of the members, is shown in FIG. 1. A thermal plastic material 3 is heated and melted on a lower mold member 2 having a transfer surface 1 in advance by a heater 4. And then, an upper mold member 6 is lowered down on the lower mold member 2 via the substrate 5 so as to pressurize (See FIG. 1-(A)) and therefore the thermal plastic material 3 and the substrate 5 are contact-bonded (See FIG. 1-(B)). In this case, as shown in FIG. 1, since the desired configuration contains a curved surface, the thickness of the thermal plastic material 3 is different depending on parts indicated by marks “A” and “B”. As a result of this, a pressure distribution (non-uniform pressure distribution) occurs at the time of pressuring so that a load cannot be given to the entire transfer surface. Because of this, a contraction after contact bonding becomes uneven so that it is difficult to transfer the transfer surface 1 of the mold member 2 to a surface of a laminate body 7 with high precision.
FIG. 2 is a schematic view of another example of the related art manufacturing method of the plastic laminate body. More specifically, a case where the substrate 5 is processed in advance to be curved is used for pressurizing is shown in FIG. 2. In this case, however, as shown in FIG. 2, if the substrate 5 and the lower mold member 2 having the transfer surface 1 are not positioned with high precision, the thickness of the thermal plastic material 3 is different depending on parts indicated by marks “C” and “D”. Hence, it is still difficult to sufficiently reduce the pressure distribution at the time of pressuring. In addition, even if the substrate 5 and the lower mold member 2 having the transfer surface 1 are positioned with high precision, in a case where configuration error between the substrate 5 and the transfer surface 1 of the lower mold member 2 differs depending on positions, there is still uneven pressure distribution like the case shown in FIG. 1.
That is, if particularly the desired configuration is a curved surface, there is an uneven pressure distribution at the time of pressurizing due to the configuration error of the plastic substrate and the member having the transfer surface, so that the contraction after contact bonding becomes uneven. This causes a problem in that it is difficult to transfer the transfer surface with high precision.